U.S. patent application number 11/728533 was filed with the patent office on 2007-10-04 for imaging apparatus, video signal processing circuit, video signal processing method and computer program product.
Invention is credited to Yoshiaki Nishide.
Application Number | 20070229682 11/728533 |
Document ID | / |
Family ID | 38558305 |
Filed Date | 2007-10-04 |
United States Patent
Application |
20070229682 |
Kind Code |
A1 |
Nishide; Yoshiaki |
October 4, 2007 |
Imaging apparatus, video signal processing circuit, video signal
processing method and computer program product
Abstract
A video signal processing circuit converting a color image
represented using a plurality of primary color signals into a
monocolor image is provided. The video signal processing circuit
includes: a chroma adjustment unit adjusting the chroma of the
plurality of input primary color signals; a gain correction unit
provided for each of the primary color signals, correcting gain on
the primary color signals whose chroma is adjusted in the chroma
adjustment unit; and a control unit instructing the chroma
adjustment unit to adjust the chroma and instructing each of the
gain correction units to correct the gain.
Inventors: |
Nishide; Yoshiaki; (Osaka,
JP) |
Correspondence
Address: |
FROMMER LAWRENCE & HAUG LLP
745 FIFTH AVENUE
NEW YORK
NY
10151
US
|
Family ID: |
38558305 |
Appl. No.: |
11/728533 |
Filed: |
March 26, 2007 |
Current U.S.
Class: |
348/255 ;
348/E9.047; 348/E9.054 |
Current CPC
Class: |
H04N 9/67 20130101; H04N
1/40012 20130101; H04N 9/69 20130101; H04N 1/6027 20130101 |
Class at
Publication: |
348/255 |
International
Class: |
H04N 5/20 20060101
H04N005/20 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 28, 2006 |
JP |
P2006-088735 |
Claims
1. An imaging apparatus comprising: a video signal processing
circuit converting a color image represented using a plurality of
primary color signals into a monocolor image, said video signal
processing circuit including a chroma adjustment unit adjusting the
chroma of the plurality of input primary color signals; a gain
correction unit provided for each of said primary color signals,
correcting gain on the primary color signals whose chroma is
adjusted in said chroma adjustment unit; and a control unit
instructing said chroma adjustment unit to adjust the chroma, and
instructing each of said gain correction units to correct the
gain.
2. An imaging apparatus according to claim 1, wherein: said video
signal processing circuit includes a memory unit to store
correction patterns setting the contents of gain correction; and
said gain correction unit acquires the correction pattern,
corresponding to the instruction supplied from said control unit,
from said memory unit, and corrects the gain on said primary color
signals based on said correction pattern.
3. An imaging apparatus according to claim 2, wherein: said gain
correction unit is configured using a gamma correction function of
a gamma correction circuit included in said imaging apparatus; and
said memory unit stores correction patterns including the contents
of said gamma correction and contents of said gain correction.
4. An imaging apparatus according to claim 1, wherein: said chroma
adjustment unit is configured using a luminance signal generating
function of a luminance adjustment circuit included in said imaging
apparatus.
5. An imaging apparatus according to claim 4, wherein said chroma
adjustment unit includes: a luminance generation circuit generating
luminance signals from the plurality of input primary color
signals; a color difference generation circuit generating a color
difference signal corresponding to each of the primary color
signals by subtracting the luminance signal generated in said
luminance generation circuit from each of the primary color
signals; a color difference gain adjustment circuit adjusting the
gain on each of the primary color signals generated in said color
difference generation circuit in accordance with the instruction
supplied from said control unit; and an output circuit adding said
luminance signal to each of the color difference signals whose gain
is adjusted in said color difference gain adjustment circuit and
outputting a resultant signal.
6. A video signal processing circuit converting a color image
represented using a plurality of primary color signals into a
monocolor image, comprising: a chroma adjustment unit adjusting the
chroma of the plurality of input primary color signals; a gain
correction unit provided for each of said primary color signals,
correcting gain on the primary color signals whose chroma is
adjusted in said chroma adjustment unit; and a control unit
instructing said chroma adjustment unit to adjust the chroma and
instructing each of said gain correction units to correct the
gain.
7. A video signal processing method of converting a color image
represented using a plurality of primary color signals into a
monocolor image, comprising the steps of: performing chroma
adjustment instructed on the plurality of primary color signals;
and performing gain correction separately instructed on each of the
primary color signals whose chroma is adjusted.
8. A computer program product converting a color image represented
using a plurality of primary color signals into a monocolor image,
causing a computer to execute: chroma adjustment processing
instructed on the plurality of primary color signals; and gain
correction processing separately instructed on each of the primary
color signals whose chroma is adjusted.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] The present invention contains subject matter related to
Japanese Patent Application JP 2006-088735 filed in the Japanese
Patent Office on Mar. 28, 2006, the entire contents of which being
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a video signal processing
circuit for converting a color image into a monocolor image in
which a specific color is adjusted to desired chroma, an imaging
apparatus including the video signal processing circuit, a video
signal processing method and a computer program product.
[0004] 2. Description of the Related Art
[0005] There have been known several methods for changing a color
image captured with an imaging apparatus such as a video camera
into the image of a certain color tone. For example, monocolor
processing has been typically used for video cameras as a method of
representing an image as if the image was captured using a monotone
film. Particularly, a function of changing a captured image into
the image of a sepia tone as if the image was captured using a film
is included in various imaging apparatuses.
[0006] Japanese Unexamined Patent Application Publication No.
2000-105820 discloses a method of generating a monotone image, for
example. This method includes the steps of acquiring distribution
of luminance equivalent values of respective pixels constituting an
image, deriving a corresponding relationship in luminance
conversion if any improvement is allowed in the luminance
distribution, and generating a monotone image having luminance of
the pixels converted based on the corresponding relationship.
SUMMARY OF THE INVENTION
[0007] FIG. 1 shows monocolor processing typically performed in
related art, in which primary color signals of red (R), green (G)
and blue (B) obtained by using image sensors are input into a
luminance generation circuit 201 to calculate luminance signals,
and gain on each color is applied to the luminance signals in gain
modulation circuits 202, 203 and 204. Though a circuit
configuration is comparatively simplified, colors may remain when
the luminance is saturated. There, on the contrary, may be another
processing of controlling such luminance saturation; however, it is
basically difficult to determine the representation of an image
when luminance being saturated. For example, it is difficult to
determine whether a white portion in the original image before the
monocolor processing is represented also in white after the
monocolor processing or represented in sepia. In such case, a color
tone of monocolor images is determined by manufacturers
manufacturing imaging apparatuses, and therefore users have limited
flexibility in adjusting the color tone.
[0008] In addition, there is a method of mixing original signals
with the signals on which monocolor processing is performed as
typical monocolor processing, in the case of obtaining such
representation as using a faded film; however, there is a
possibility that color still remains on the saturated signals in
such processing, which is not preferable for users.
[0009] It is desirable to perform highly flexible color tone
adjustment processing on color images.
[0010] According to an embodiment of the present invention, in the
case where a color image represented with a plurality of primary
color signals is converted into a monocolor image, saturation is
first adjusted on the plurality of primary color signals based on
instructions supplied from an operation unit or the like, and
subsequently, gain correction indicated to each of the primary
colors is performed on the saturation-adjusted primary color
signals.
[0011] Monocolor images described herein include a monochrome image
having gradation of black and white, a monocolor image of single
color with saturation adjusted, and further an image made of a
plurality of colors.
[0012] With the above-described configuration, since saturation of
each of the primary color signals is first adjusted and afterward
the gain correction is performed on each of the saturation-adjusted
primary color signals, a color tone can independently be adjusted
on each color.
[0013] According to an embodiment of the present invention, highly
flexible color tone adjustment processing can be performed on color
images.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a diagram illustrating monocolor processing in
related art;
[0015] FIG. 2 is a block diagram showing an example of
configuration of a video camera according to an embodiment of the
present invention;
[0016] FIG. 3 is a diagram showing an example of configuration of a
color adjustment circuit of the video camera shown in FIG. 2;
[0017] FIG. 4 is a diagram showing an example of non-linear gain
curves (1) according to an embodiment of the present invention;
[0018] FIG. 5 is a diagram showing an example of non-linear gain
curves (2) according to an embodiment of the present invention;
[0019] FIG. 6 is a diagram showing an example of non-linear gain
curves (3) according to an embodiment of the present invention;
[0020] FIG. 7 is a diagram showing an example of configuration of a
gamma correction circuit in the video camera shown in FIG. 2;
[0021] FIG. 8 is a diagram showing an example of gamma
characteristics according to another embodiment of the present
invention;
[0022] FIG. 9 is a diagram showing gain curves of non-linear
component gamma characteristics according to another embodiment of
the present invention;
[0023] FIG. 10 is a diagram showing an example of output signals
after non-linear processing according to another embodiment of the
present invention; and
[0024] FIG. 11 is a diagram showing an example of a saturation
adjustment circuit in the color adjustment circuit shown in FIG.
3.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] Preferred embodiments of the present invention are
hereinafter described with reference to accompanied drawings. It
should be noted that herein "monocolor processing" refers to
processing of converting a ordinary color image into a monocolor
image.
[0026] FIG. 2 is a block diagram showing a basic configuration of a
video camera to which an imaging apparatus according to an
embodiment of the present invention is applied. Filters to resolve
an optical image captured by a lens (not illustrated) into three
primary color images of red (R), green (G) and blue (B) are mounted
in the video camera shown in FIG. 2 prior to three image sensors 1,
2 and 3, each of which includes an imaging device using CCD (Charge
Coupled Device) and the like. Subject image light is incident on
light receiving portions of the image sensors 1, 2 and 3 via the
filters after passing through an optical system such as a lens not
illustrated, and a photoelectric conversion is performed on red,
green and blue images, separately. Although three image sensors for
red, green and blue are provided in this embodiment, it should be
appreciated that image sensors corresponding to, for example, four
colors may be provided without limiting to this embodiment.
[0027] The image sensors 1, 2 and 3 perform the photoelectric
conversion and generate primary color signals forming video signals
from the subject image, respectively, and subsequently supply the
three primary color signals (signal R, signal G and signal B) to
video amplifiers 4, 5 and 6, respectively. It should be noted that
the above-described video signals can be applied to a still image,
as well as a moving image.
[0028] The video amplifiers 4, 5 and 6 are gain adjusters, and AGC
(Automatic Gain Control) circuits or the like can be applied, for
example. The video amplifiers 4, 5 and 6 adjust gains of the
primary color signals, and supply the gain-adjusted primary color
signals to A/D converters 7, 8 and 9, respectively. The A/D
converters 7, 8 and 9 convert input analog signals into digital
signals supplied to a video signal processing unit 16.
[0029] The video signal processing unit 16 according to this
embodiment includes a correction circuit 10, a gain adjustment
circuit 11, a color adjustment circuit 12, a luminance adjustment
circuit 13, a gamma correction circuit 14 and an output signal
generation circuit 15. First, the primary color signals R, G and B
adjusted and quantized to appropriate levels by using the
above-described video amplifiers 4, 5, 6 and A/D converters 7, 8, 9
are input into the correction circuit 10 in the video signal
processing unit 16.
[0030] The correction circuit 10 performs signal processing such as
predetermined interpolation processing with filter processing and
shading processing on the input three primary color signals
supplied to the gain adjustment circuit 11.
[0031] The gain adjustment circuit 11 adjusts gains of the three
primary color signals input from the correction circuit 10 to
appropriate levels, and supplies the adjusted three primary color
signals to the color adjustment circuit 12.
[0032] The color adjustment circuit 12 is a video signal processing
circuit according to an embodiment of the present invention,
adjusting (correcting) color tones of the three primary color
signals input from the gain adjustment circuit 11 to desired color
tones, and supplying the adjusted three primary color signals to
the luminance adjustment circuit 13.
[0033] The luminance adjustment circuit 13 extracts luminance
signals from the primary color signals input from the color
adjustment circuit 12 so that video signals fall in a predetermined
range, controls an amplitude characteristic of the luminance
signals in a high-luminance region to narrow a dynamic range of the
output from each image sensor, and supplies the luminance signals
to the gamma correction circuit 14.
[0034] The gamma correction circuit 14 performs correction
corresponding to a gamma characteristic of a monitor (receiver)
such as CRT (Cathode Ray Tube) on each of the three primary color
signals input from the luminance adjustment circuit 13, and
supplies the gamma-corrected primary color signals to the output
signal generation circuit 15.
[0035] The output signal generation circuit 15 converts the three
primary color signals input from the gamma correction circuit 14
into an ultimate video-signal output format and outputs the
converted primary color signals to the outside. For example, the
output signal generation circuit 15 has a function of serving as an
encoder converting the three primary color signals into
color-difference signals and modulating the color-difference
signals by using sub-carrier signals (not illustrated) to conform
to NTSC (National Television System Committee) standard, PAL (Phase
Alternating Line) standard, or the like. Further, in the case where
video signals should be output as analogue signals, the output
signal generation circuit 15 includes a D/A converter that converts
quantized color-difference signals output from the above-described
encoder circuit into analogue signals.
[0036] A microcomputer 17 is an example of a control unit that
controls respective circuits constituting the video signal
processing unit 16. Further, the microcomputer 17 controls
operation of an optical system such as a lens (not illustrated) and
operations of the video amplifiers 4, 5 and 6. An operation unit 18
includes button keys provided on the video camera, soft keys
allocated to icons displayed on a monitor screen mounted on the
video camera, and the like, inputting an operation signal
corresponding to such operation to the microcomputer 17 from the
operation unit 18 via an interface not illustrated. The
microcomputer 17 performs predetermined operations and control on
each circuit using a computer program stored in a non-volatile
memory unit such as an internal ROM (Read Only Memory) based on an
operation signal input by a user operating the operation unit 18,
or based on predetermined settings defined in advance and the
like.
[0037] Further, the microcomputer 17 connects to a drive circuit
(not illustrated) according to need, and reads computer programs
from a magnetic disk, optical disk, magneto-optical disk,
semiconductor memory, or the like suitably mounted thereto and
installs the programs in RAM incorporated in the microcomputer 17
as needed.
[0038] As described above, photoelectric conversion is performed on
a subject image in the image sensors 1, 2 and 3 to generate primary
color signals of red (R), green (G) and blue (B), subsequently, the
generated primary color signals are adjusted and quantized to
analogue signals at appropriate levels, and converted into digital
signals using the video amplifiers 4, 5, 6 and A/D converters 7, 8,
9 in the video camera. Appropriate correction and gain adjustment
processing are performed on each of the quantized primary color
signals in the correction circuit 10 and gain adjustment circuit
11, and subsequently, each primary color signal is input into the
color adjustment circuit 12. Each of the primary color signals
input into the color adjustment circuit 12 is adjusted to a desired
color tone based on an instruction supplied from the microcomputer
17 and is input into the luminance adjustment circuit 13. Further,
appropriate luminance reduction processing is performed in the
luminance adjustment circuit 13 on each of the primary color
signals, and afterward, the signals are input into the gamma
correction circuit 14. The gamma-corrected primary color signals
are converted into signals of the ultimate video signal output
format to be output from the output signal generation circuit
15.
[0039] The color adjustment circuit 12 is described in detail. FIG.
3 shows an example of configuration of the color adjustment circuit
12. The color adjustment circuit 12 according to this embodiment
includes a chroma adjustment circuit 21, a non-linear gain
modulation circuit 22 for signal R (channel R), a non-linear gain
modulation circuit 23 for signal G (channel G) and a non-linear
gain modulation circuit 24 for signal B (channel B). The color
adjustment circuit 12 performs the non-linear operation separately
on the video signals each having different color information, in
other words, on the primary color signals R, G, and B having
adjusted chroma (also called saturation).
[0040] The chroma adjustment circuit 21 is an example of a chroma
adjustment unit adjusting the chroma of the input primary color
signals based on the instruction supplied from the microcomputer
17, and outputting the primary color signals to the corresponding
non-linear gain modulation circuits 22, 23 and 24,
respectively.
[0041] The non-linear gain modulation circuits 22, 23 and 24 are
examples of gain adjustment units that correct the gain on the
input primary color signals using a gain modulation pattern
(correction pattern) determined by the instruction supplied from
the microcomputer 17, and the corrected primary color signals are
output. Gain correction is performed by non-linear processing in
this embodiment.
[0042] Upon inputting the primary color signals R, G and B into the
chroma adjustment circuit 21 from the gain adjustment circuit 11
(see FIG. 2) in the color adjustment circuit 12, the chroma
adjustment circuit 21 adjusts the chroma of the primary color
signals based on the instruction supplied from the microcomputer
17, and supplies the chroma-adjusted primary color signals to the
corresponding non-linear gain modulation circuits 22, 23 and 24,
respectively. Each of the non-linear gain modulation circuits 22,
23 and 24 performs the non-linear processing to obtain a desired
gain on each of the chroma-adjusted primary color signals by
referring to the gain modulation pattern, and outputs the resultant
signals to the subsequent luminance adjustment circuit 13 (see FIG.
2). It should be noted that there may be a color (primary color
signal) on which the non-linear processing is not performed
depending on gain modulation patterns.
[0043] Thus, the chroma is adjusted on the input three primary
color signals in the chroma adjustment circuit 21, and
subsequently, the non-linear processing is performed separately on
respective primary color signals R, G and B in the non-linear gain
modulation circuits 22, 23 and 24 in the color adjustment circuit
12. FIG. 4 shows an example of a gain modulation pattern that is
referred to when the non-linear gain modulation circuits perform
the non-linear processing.
[0044] As shown in FIG. 4, a horizontal axis indicates a signal
level (luminance level) of a primary color signal input into the
color adjustment circuit 12, and a vertical axis indicates a signal
level of the primary color signal after the gain adjustment. "0"
represents the signal level of 0%, which is black, and "1"
represents the signal level of 100%, which is white in this
example. Signal levels in the range of "0" to "1" can be
represented, for example, with 256 values using 8-bit
information.
[0045] A curve 31 indicates a relationship between the input signal
level and output signal level of the signal R; a curve 32 indicates
a relationship between the input signal level and output signal
level of the signal G; and a curve 33 indicates a relationship
between the input signal level and output signal level of the
signal B. The example shown in FIG. 4 represents a gain adjustment
pattern in which only the channel R is emphasized without
performing the non-linear processing on the channels G and B.
Although the curves (straight lines in actuality) 32 and 33 are
identical, those two curves are slightly differed for the
convenience of explanation.
[0046] As shown in FIG. 4, the non-linear processing is performed
on each of the chroma-adjusted primary color signals separately in
the color adjustment circuit 12. Accordingly, the gain of the
channel R can be emphasized in an intermediate range, while
retaining the input signal states in the vicinity of black and
white, that is, the signal levels "0" and "1". In other words, the
monocolor representation only using red can be obtained.
[0047] With the application of such function performed by the color
adjustment circuit 12, the microcomputer 17 sets a non-linear gain
modulation pattern shown in FIG. 5, for example, thereby enabling
representation of various colors to be obtained with more
flexibility. As shown in FIG. 5, a curve 41 indicates the
relationship between the input signal level and output signal level
of the signal R; a curve 42 indicates the relationship between the
input signal level and output signal level of the signal G; and a
curve 43 indicates the relationship between the input signal level
and output signal level of the signal B. The example shown in FIG.
5 represents a gain adjustment pattern in which only the channels R
and B are emphasized while the channel G is controlled, and
particularly, the channel R is emphasized in this pattern.
[0048] Applying the above-described non-linear gain adjustment
processing to primary color signals with chroma controlled to the
extent of about one-severalth in the chroma adjustment circuit 21,
such representation as a faded picture with dark red and light
green can be obtained.
[0049] Furthermore, black-and-white monochrome representation can
also be obtained by almost eliminating the chroma in the chroma
adjustment circuit 21.
[0050] FIGS. 4 and 5 are diagrams showing examples of the gain
modulation patterns in which the same color is represented over the
whole image. However, such image representation that the color
changes depending on the input signal level can be obtained using a
gain modulation curve with the channel R emphasized at a higher
level of the input signal and the channel B on the contrary
emphasized at a lower level thereof, for example. FIG. 6 shows an
example of the gain modulation pattern to obtain such image
representation.
[0051] As shown in FIG. 6, a curve 51 indicates the relationship
between the input signal level and output signal level of the
signal R; a curve 52 indicates the relationship between the input
signal level and output signal level of the signal G; and a curve
53 shows the relationship between the input signal level and output
signal level of the signal B. The example shown in FIG. 6
represents a gain adjustment pattern in which the gain modulation
curve 51 for the channel R rises only at a higher level and on the
contrary the gain modulation curve 53 for channel B drops only at a
lower level. With the non-linear processing being performed using
such gain modulation pattern, a dark portion of the image includes
output signals that the channel B (blue) is controlled and a light
portion thereof includes output signals that the channel R (red) is
dominant.
[0052] As described in the above example, the non-linear processing
in the non-linear gain modulation circuits is varied corresponding
to the level of the input primary color signals. Accordingly, an
image having different color intensities depending on the level of
the primary color signals can be output to a subsequent
circuit.
[0053] As described above, adjustment of the chroma of primary
color signals in the color adjustment circuit 12 is followed by the
non-linear operation performed on the chroma-adjusted primary color
signals for respective colors, causing highly flexible color tone
adjustment processing to be obtained.
[0054] Specifically, upon inputting an operation signal into the
microcomputer 17 by the user operating the operation unit 18, the
microcomputer 17 outputs the chroma adjustment instruction and gain
modulation instruction corresponding to the operation by the user
to the chroma adjustment circuit 21 and non-linear gain modulation
circuits 22, 23 and 24. Further, each of the primary color signals
is adjusted to a desired chroma in the chroma adjustment circuit 21
based on the instruction supplied from the microcomputer 17, and
afterward, the non-linear processing is performed separately on
respective primary color signals in the non-linear gain modulation
circuits 22, 23 and 24 based on the instruction supplied from the
microcomputer 17, thereby providing image representation desirable
for the user.
[0055] Here, a gain modulation pattern corresponding to a display
mode such as "sepia" set as default in the video camera may be
edited into a color tone preferable for the user, and the gain
modulation pattern may be stored in a non-linear table described
later. As a result, when the user selects, for example, the "sepia"
mode by operating the soft key on the monitor, the edited gain
modulation pattern corresponding to the "sepia" is selected, and
the image adjusted to the desired "sepia" tone is represented.
Further, the user may operate the operation unit 18 to perform a
real time color-tone adjustment operation on each of the primary
color signals for the image displayed on the monitor.
[0056] Curve fitting using a curve, broken line approximation using
straight lines, and the like are used as methods for obtaining a
circuit to perform such non-linear processing; however, a circuit
configuration tends to be large in any of the methods, in order to
keep the accuracy within an appropriate range. Therefore, there is
proposed a method of performing the gain modulation processing in
the gamma correction circuit 14 that is also a non-linear operation
circuit. The gamma correction processing circuit using the broken
line approximation is hereinafter described as an example, with
reference to FIGS. 7 to 10.
[0057] FIG. 8 shows the gamma correction processing based on the
broken line approximation, in which a difference between a gamma
value of a gamma correction curve indicated by a curve 73 and a
linear characteristic value (linear value) indicated by a curve 71
is treated as a gamma correction value, and the broken line
approximation is performed to obtain a non-linear curve 72
indicating an amount of level change represented by the difference.
Data on respective line segments are obtained as final gamma
correction values. Japanese Unexamined Patent Application
Publication No. H09-172562 discloses a specific example of such
gamma correction processing proposed by the applicant of this
invention. Here, the contents thereof are briefly explained.
[0058] FIG. 7 shows an example of configuration of one channel in
the gamma correction circuit 14 according to an embodiment of the
present invention. As shown in FIG. 7, one channel of the gamma
correction circuit includes a gain and offset calculation circuit
61, a non-linear component generation circuit 63 and a non-linear
component addition circuit 66. The gamma correction circuit 14
includes the circuit having the configuration shown in FIG. 7 for
each of the three channels R, G and B.
[0059] As shown in FIG. 7, a primary color signal input from the
luminance adjustment circuit 13 is input into the gain and offset
calculation circuit 61. The gain and offset calculation circuit 61
extracts a gain adjusting coefficient and offset amount
corresponding to the input signal level from a non-linear table 62
based on the instruction supplied from the microcomputer 17.
[0060] The non-linear table 62 includes contents of non-linear
processing (a range of the input signal level to which the
non-linear processing is performed, and gain amount) determined by
the microcomputer 17, and inclination data a and section data b of
the straight line represented by a linear equation "Y=aX+b" that is
tangent to the non-linear curve 72 at the time, both the contents
and data being correlated. The non-linear table 62 is stored in a
non-volatile memory device such as a ROM (not illustrated), and is
loaded in a RAM to be referred to by the gain and offset
calculation circuit 61 reading the data corresponding to the
instruction. It should be noted that the non-linear table 62 is
also called a mapping table or look-up table.
[0061] The gain and offset calculation circuit 61 refers to the
non-linear table 62 and reads the inclination data a and section
data b for each of the signal levels of the input primary color
signals, supplying the inclination data a as the gain adjustment
coefficient and the section data b as the offset amount to the
non-linear component generation circuit 63.
[0062] The non-linear component generation circuit 63 includes a
multiplier 64 and an adder 65, the multiplier 64 multiplying an
input signal X by the gain coefficient a and the adder 65 adding
the offset amount b to an output aX from the multiplier 64,
generating a non-linear component relating to the gamma correction
and supplying the generated non-linear component to the non-linear
component addition circuit 66. The signals supplied from the
non-linear component generation circuit 63 correspond to the curve
72 in FIG. 8.
[0063] The non-linear component addition circuit 66 includes an
adder 67 adding the signal output from the non-linear component
generation circuit 63 to the input signal supplied to the output
signal generation circuit 15. The gamma correction processing
performs such non-linear processing on the three primary color
signals R, G and B.
[0064] The gain and offset amount for the input signal are
calculated by referring to the non-linear table 62 in order to
generate the non-linear component. Further, the calculated gain and
offset amount is computed in the non-linear component generation
circuit 63 to generate the non-linear component, and finally the
generated non-linear component is added to the input signal (linear
component) in the non-linear component addition circuit 66, thereby
completing the gamma correction processing in the gamma correction
circuit having the configuration described above.
[0065] As described above, the gamma correction circuit generates
the non-linear component (curve 72) using the linear component
(curve 71) of the input signal (primary color signal), and those
components are added to output the gamma correction curve 73. Here,
this non-linear component is observed, and different gain
modulation patterns are applied to the input signals R, G and B
respectively, thereby obtaining the non-linear processing according
to an embodiment of the present invention. Specifically, the gain
modulation patterns considered to be used in the non-linear
processing according to the embodiment of the present invention are
prepared for the gamma correction processing, and are stored in the
non-linear table 62. Subsequently, the instruction on color tone
adjustment (non-linear gain adjustment) is supplied from the
microcomputer 17, and in accordance with the contents of the color
tone adjustment instructed, the gain and offset calculation circuit
61 refers to the gain modulation pattern corresponding to the
contents of the instruction. Further, the gain and offset
calculation circuit 61 executes the non-linear processing relating
to the gamma correction and color tone adjustment on each of the
primary color signals based on the gain modulation pattern. FIG. 9
shows an example of the gain modulation pattern of the non-linear
component.
[0066] As shown in FIG. 9, a curve 81 indicates the relationship
between the input signal level and output signal level in the
non-linear component of the signal R; a curve 82 indicates the
relationship between the input signal level and output signal level
in the non-linear component of the signal G; and a curve 83
indicates the relationship between the input signal level and
output signal level in the non-linear component of the signal B. As
shown in FIG. 9, the non-linear component (curve 81) of the channel
R rises higher than the other channels and is emphasized in a
middle range. FIG. 10 shows the final output signals obtained based
on the gain curves of the non-linear components shown in FIG.
9.
[0067] As shown in FIG. 10, a curve 91 indicates the relationship
between the input signal level and output signal level of the
signal R; a curve 92 indicates the relationship between the input
signal level and output signal level of the signal G; and a curve
93 indicates the relationship between the input signal level and
output signal level of the signal B. As shown in FIG. 10, only a
middle range of the channel R gamma characteristic curve 91 rises
and, as a result, only the channel R can be emphasized and
represented on the monitor side.
[0068] Here, in the case of obtaining the video signal processing
(monocolor processing) according to an embodiment of the present
invention using the gamma correction circuit as described above, an
ordinary gamma characteristic (non-linear light-emitting output
characteristic) is inversely converted on the monitor side.
Therefore, the color representation in the actual monocolor
processing is obtained by inversely converting the gain modulation
pattern to be set. More specifically, the gain modulation patterns,
when using the gamma correction non-linear processing circuit, are
set in consideration of the gamma characteristic on the monitor
side, differing from the gain modulation patterns used in the
non-linear gain modulation circuits 22, 23 and 24 shown in FIG.
3.
[0069] In the case of thus using the gamma correction circuit for
the video signal processing according to an embodiment of the
present invention, similarly to the previous description, also
highly flexible color tone adjustment processing can be performed
to obtain image representation that emphasizes various colors and
image representation that emphasizes different colors at the lower
level and higher level of the input signal respectively by
combining a plurality of colors.
[0070] Next, the chroma adjustment circuit 21 is also described in
detail. There is proposed chroma adjustment processing of
generating the luminance signals from the input primary color
signals, adjusting gains on signals resulted from subtracting the
luminance signals from the respective primary color signals, and
afterward performing an operation of adding the luminance signals
again.
[0071] FIG. 11 shows an example of a circuit configuration to
obtain the above-described chroma adjustment processing. As shown
in FIG. 11, the chroma adjustment circuit according to this
embodiment includes a luminance generation circuit 101, a color
difference generation circuit 102, a color difference gain
adjustment circuit 103 and an output circuit 104.
[0072] The luminance generation circuit 101 uses a matrix circuit
to generate the luminance signals from the primary color signals R,
G and B.
[0073] The color difference generation circuit 102 performs an
operation of subtracting the luminance signals generated in the
luminance generation circuit 101 from the input primary color
signals R, G and B, and generating the color difference
signals.
[0074] The color difference gain adjustment circuit 103 performs an
operation of multiplying the color difference signals of respective
channels generated in the color difference generation circuit 102
by a gain adjustment coefficient (k) 105 set by the
microcomputer.
[0075] The output circuit 104 performs processing of adding the
luminance signals generated in the luminance generation circuit 101
to respective color difference signals having the gain adjusted in
the color difference gain adjustment circuit 103, outputting the
resultant signals to subsequent circuits.
[0076] The luminance signals are first generated from the primary
color signals R, G and B input into the luminance generation
circuit 101 in the chroma adjustment circuit having the
above-described configuration. The luminance signals are subtracted
from respective primary color signals in the color difference
generation circuit 102 to generate the color difference signals
R-Y, G-Y and B-Y corresponding to the primary color signals
respectively. Subsequently, each of the color difference signals is
multiplied by the gain adjustment coefficient (k) in the color
difference gain adjustment circuit 103 to adjust the gain. Finally,
the luminance signals are again added to respective gain-adjusted
color difference signals in the output circuit 104, and the video
signals R', G' and B' each having the adjusted chroma and the same
luminance are output to the outside.
[0077] The video signals R', G' and B' finally output from the
output circuit 104 are described as follows:
R'=(R-Y).times.k+Y
G'=(G-Y).times.k+Y
B'=(B-Y).times.k+Y
[0078] In the case of the gain coefficient k being "0", for
example, a monotone representation of black and white is obtained
with output primary color signals. Further, in the case of the gain
coefficient k being "0.5", a color tone with half the color
remaining in each of the output primary color signals is
obtained.
[0079] The adjustment operation itself is not particularly large in
terms of volume, but having a dedicated circuit causes an increase
in circuit scale of the whole video signal processing unit 16.
Therefore, part of the luminance adjustment circuit 13 such as the
function of extracting the luminance signal, for example, is
applied to this processing, thereby enabling the processing using a
known circuit to be performed similarly to the non-linear
processing using the gamma correction circuit, and preventing the
increase in circuit scale.
[0080] As heretofore described, an imaging apparatus such as a
video camera has the configuration in which chroma of each of
primary color signals R, G and B is adjusted, and afterward the
non-linear operation is performed separately on each of the
chroma-adjusted primary color signals. Accordingly, highly flexible
color tone adjustment processing can be performed on images.
Further, the monocolor expression based on black and white is also
possible by completely reducing the chroma.
[0081] In addition, the luminance adjustment circuit 13 and the
gamma correction circuit 14 are respectively used for or applied to
the chroma adjustment function and the non-linear processing
function for respective colors performed in the color adjustment
circuit 12, thereby enabling the color tone adjustment processing
according to an embodiment of the present invention to be performed
without adding a specific circuit. Accordingly, increase in circuit
scale can be controlled to a minimum.
[0082] It should be noted that the above-described processing in
the video signal processing unit 16 (refer to FIG. 2) can be
executed by hardware, and also can be executed by software. In the
case of executing the series of processing using the software, a
program code constituting the software is stored in a memory unit
such as a ROM incorporated in the microcomputer 17. Particularly,
in the case of executing by the software the series of video signal
processing (monocolor processing) according to an embodiment of the
present invention, described using FIGS. 3, 7 and 11, the video
signal processing unit 16 may include an extended monocolor
processing function according to an embodiment of the present
invention with newly installing in the memory unit the program code
to execute the processing.
[0083] It should be appreciated that the embodiments of the present
invention are also implemented by providing a recording medium
having a recorded program code of the software performing the
above-described function according to the embodiment to a system or
apparatus, and by reading and executing the program code stored in
the recording medium using a computer (computing unit) in the
system or apparatus.
[0084] A recording medium such as a floppy disk, hard disk, optical
disk, magneto-optical disk, CD-ROM, CD-R, magnetic tape,
non-volatile memory card, ROM, and the like can be used as the
recording medium for supplying the program code.
[0085] Further, the function according to the above-described
embodiments is obtained not only by executing the program code read
by the computer, but also by executing part or all of actual
processing using OS or the like operating on the computer based on
an instruction of the program code.
[0086] Furthermore, an example in which an imaging apparatus
according to an embodiment of the present invention is applied to
the video camera is described in the above embodiments; however, an
embodiment of the present invention can be widely applied to
various apparatuses without limiting to the video camera, and may
be applied to a digital still camera, color image scanner, or other
apparatuses having an equivalent function, for example. Moreover, a
receiver receiving a video signal from an imaging apparatus may
have the video signal processing function according to an
embodiment of the present invention, and the video signal
processing, specifically, the monocolor processing, can be
performed on the receiver side.
[0087] It should be understood by those skilled in the art that
various modifications, combinations, sub-combinations and
alterations may occur depending on design requirements and other
factors insofar as they are within the scope of the appended claims
or the equivalents thereof.
* * * * *